(1) Field of the Invention
The present invention relates to controls and standards for assays and methods for manufacturing the controls and standards. The controls or standards comprise a porous carrier material which has quantitatively reversibly absorbed thereon an analyte for the control or standard wherein the analyte is not significantly degraded over time while it is absorbed to the porous carrier material. Preferably, the controls and standards are provided as a control strip in which the porous carrier material is adhered to the distal end of a support member. The controls and standards are stable for prolonged periods of time and are useful for immunoassays which detect bacteria, fungi, viruses, and other antigens.
(2) Description of Related Art
Controls or standards are important components for most analytic assays. For many assays, particularly assays which use biological controls or standards, the controls or standards are provided as a freeze-dried material which is reconstituted to the proper concentration in an aqueous solution appropriate for the particular material. An aliquot of the reconstituted material is then diluted in an aqueous solution appropriate for the assay. The remainder of the reconstituted material is usually divided into aliquots which are then stored frozen or for particularly unstable material, discarded. For other assays that use biological material, the controls or standards are provided as a frozen solution or suspension which prior to use is thawed and an aliquot removed which is then diluted to the appropriate concentration for use in the assay. The remainder of the thawed material is refrozen for future use.
Regardless with how the material for the controls or standards is provided, there are two problems. The first is that the actual concentration of the material will vary from assay to assay because of pipetting errors which can occur during reconstitution of the material, dilution of the material, and aliquoting and dispensing the material. This uncertainty can make it difficult to correlate results from assay to assay, which can be important when the assays are quantitative. This problem is particularly acute when the assays are performed by different people.
The second problem is related to storage and stability of the material. Many biological materials are unstable when stored for extended periods either lyophilized or in aqueous solutions at a temperature above freezing, particularly when diluted to a concentration suitable for the assay. When stored at temperatures below freezing, many biological materials are susceptible to degradation when they are repeatedly frozen and then thawed. Therefore, the actual concentration of the biological material decreases over time which introduces an uncertainty into the assay that can make it difficult to correlate results from assay to assay, which can be important when the assays are quantitative. A further disadvantage is that storing frozen aqueous solutions of biological material requires expensive freezers that are preferably able to store the biological material at −80° C.
The prior art has attempted to address the above problems either by introducing methods for drying and storing biological materials which do not involve lyophilization or freezing or methods which attempt to avoid errors introduced by pipetting.
The following U.S. Patents disclose methods for drying a biological material without using lyophilization: U.S. Pat. No. 4,684,615 to Hoskins; U.S. Pat. Nos. 4,891,319 and 5,149,653, both to Roser; U.S. Pat. No. 5,009,994 to McGeehan; U.S. Pat. No. 5,030,560 to Sinor et al.; U.S. Pat. No. 5,098,893 to Franks et al.; U.S. Pat. Nos. 5,200,399 and 5,290,765, both to Wettlaufer et al.; U.S. Pat. No. 5,292,507 to Charley; U.S. Pat. No. 5,547,873 to Magneson et al., U.S. Pat. Nos. 5,955,448; U.S. Pat. No. 6,008,052 to Davis et al., and, 6,313,102 B1, both to Colaco et al. In general, the above methods involve mixing the biological material in a solution comprising inter alia a carbohydrate and drying the mixture at a temperature above freezing. The methods render the material stable at temperatures above freezing.
The following also disclose methods for preserving a biological material using agents other than a carbohydrate as the stabilizing agent: U.S. Pat. No. 5,240,843 to Gibson et al.; U.S. Pat. No. 5,126,242 to Hachmann et al.; U.S. Pat. No. 5,300,424 to Hoss et al.; U.S. Pat. No. 5,728,574 to Legg; and, U.S. Pat. No. 6,165,773 to New et al.
The following U.S. patents disclose devices for providing a reagent to an assay or use as controls for an assay and methods for manufacturing the devices.
U.S. Pat. No. 3,671,400 to Cekoric, Jr. et al. discloses bacterial controls for test procedures and reagents comprising discrete droplets of a nutrient gelatin and bacteria which has been vacuum desiccated at ambient temperature onto a sterile non-adhering supporting surface.
U.S. Pat. No. 3,975,162 to Renn discloses a device for providing a measured quantity of water-soluble or water-dispersible reagent to a water-containing solid medium is provided in the form consisting essentially of a film-forming solid organic binder which is at least partly soluble in water and having dispersed therein a measured quantity of the reagent.
U.S. Pat. No. 4,234,316 to Hevy discloses a device for delivering precise measured quantities of a plurality of reagents into an assay. The device comprises a water impervious support secured to one or more faces of which are discrete and separate elements each containing a water soluble or dispersible binder which has dispersed therein the reagent. The device is contacted with the assay medium for a time sufficient to dissolve the binder to release the reagent into the assay medium.
U.S. Pat. Nos. 4,803,171 and 5,118,609, both to Baier et al. disclose a carrier fleece for use as a reagent carrier from which reagents can be dissolved in an assay such as an immunological analysis. The carrier fleece comprises cellulose-containing fibers, polymer fibers, and an organic binding agent which has a hydroxyl or ester group, or both. Preferably, the binding agent is polyvinyl alcohol or polyacrylic esters.
U.S. Pat. No. 5,403,706 to Wilk et al. discloses a carrier matrix with a dissolvably impregnated reagent. The matrix is manufactured by slurring glass fibers with an excess of water and polyvinyl alcohol and forming a layer wherein all of the glass fibers are coated with the polyvinyl alcohol. The slurry layer is dried and then impregnated with the reagent. In use, the impregnated layer is contacted with a solvent which elutes the reagent from the layer.
U.S. Pat. No. 6,008,052 to Davis et al. discloses a method for preserving cells as controls or standards in cellular analysis. The cells are fixed with a fixative, reduced with a Schiff's base reducing agent, and then dried in the presence of a protein stabilizing compound such as trehalose.
U.S. Pat. No. 6,281,044 B1 to Bogen et al. discloses quality control devices for assays which measure analytes in cells and tissue samples comprising a matrix afixed with synthetic controls in different concentrations, or different synthetic controls. The matrix preferably includes an adhesive surface on the back side which adheres the matrix to a removable backing sheet which is removed when an assay is performed on the device. In use, the matrix is reacted with the same detection reagent used in the assay.
Only of minimal interest are U.S. Pat. No. 4,734,360 to Phillips (test strip for detecting ethanol); U.S. Pat. No. 4,820,644 to Schäfer et al. (porous carrier material containing first and second components of an immune reaction precipitated thereon); U.S. Pat. No. 6,168,957 B1 to Matzinger et al. (dry phase reagent test strip for measuring the concentration of an analyte); and, European Patent Application No. 0140489 to Sakata et al. (method for stabilizing immunologically active substances immobilized on an insoluble carrier).
While there are a number of methods for preserving analytes and there are several methods for providing controls or standards to assays, there still remains a need for a method for providing controls or standards for assays which is facile and inexpensive to prepare and which provide consistent results between assays regardless of the skill of the user of the control or standards or the time which has elapsed between assays. The present invention provides a method for providing controls or standards which satisfies the above need.